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如果在十五年前，那时候我刚开始看Linux内核情景分析，看到了微软这么用心的支持Linux、甚至是在Windows上支持Linux，我可能会很激动吧。

但是现在，我只会说，哦，这样啊！

Linux on Windows有两个阶段：不支持Linux GUI应用的WSL；支持Linux GUI的 WSL2。

XDC2020上有些话题是关于WSL2的图形系统的，这里稍微摘录整理下。

OpenGL over D3D

https://www.collabora.com/news-and-blog/blog/2020/07/09/deep-dive-into-opengl-over-directx-layering/

DXIL: compiled shaders (DXIL bytecode). DXIL is essentially LLVM 3.7 bitcode with some extra metadata and validation.
NIR: Mesa will also translate GLSL shaders into an intermediate representation named NIR.

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Graphics Architecture on Windows Subsystem for Linux

https://xdc2020.x.org/event/9/contributions/610/attachments/700/1295/XDC_-_WSL_Graphics_Architecture.pdf

Linux子系统其实就是一个完全独立的运行在windows上的虚拟机。
VM提供了虚拟的显存和虚拟的GPU供Linux子系统使用。
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如果将OpenGL over D3D和Graphics Architecture on Windows Subsystem for Linux， 就可以一窥整个Windows Graphics for Linux的大概：

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And Android on WSL2 without emulator becomes possible:

https://www.reddit.com/r/bashonubuntuonwindows/comments/eofn5s/run_anbox_on_wsl_2/

About OpenGL and Vulkan interoperability

EXT_external_objects(_fd) extensions enable:

• Allocation of resources (textures, buffers) from Vulkan and sharing
  of those resources from both APIs
• Synchronization of the access to shared resources between APIs.
• Example: a VR compositor where the left and right eye images are allocated and
  displayed by Vulkan but their contents are filled by OpenGL processes.

Linux extension:
EXT_external_objects_fd (EXT_memory_object_fd, EXT_semaphore_fd):

• enables an OpenGL application to import a memory object or semaphore
  from POSIX file descriptor external handles

EXT_external_objects (EXT_memory_object, EXT_semaphore):

• enables an OpenGL application to create OpenGL objects corresponding to
  Vulkan objects (textures, buffers, semaphores) and synchronize access to
  shared objects across APIs
• extends existing GL calls that set and query properties

Reference:
https://xdc2020.x.org/event/9/contributions/620/attachments/696/1308/estea-xdc2020.pdf